And if you connect with a mobile device on the same network as the computer with the files on it, they'll automatically be transferred so you'll get them on mobile too.
Two of my favorite bands (Blind Guardian, Kamelot) put only their last couple of releases on Spotify, but with this method I can listen to their whole back catalog.
Afraid that an artist is going to pull their stuff from spotify? Acquire digital copies of that artist's work some other way, and spotify will slot them right into your playlists where the old ones used to be. I did this when SPV Records pulled Silverthorn, it was practically no work.
Even if the whole industry abandons spotify, it will still be unique and valuable as a seamless way to synchronize your music library between all devices.
I'd rather pay more in the short term, paying for individual tracks, for a solution that will work indefinitely, than set up a situation in which extreme disruption of a part of my life I'm utterly reliant on can be afflicted at a whim of a dipshit music exec who doesn't understand how people can become reliant on music or worse, understands and does it anyway because it'll make him more money.
Whereas my personal catalog will never stop supporting my use cases.
It's totally your prerogative to not use spotify or other music streaming services, I'm just saying fear of imminent market apocalypse isn't really a good reason to deny all of the upsides.
The ones already shut down or folded into different companies with different priorities include Rhapsody, Beatport, Rdio, Last.fm's streaming offering, and the aforementioned Zune. Forgive me if I'm a little cautious and not willing to depend on the magic of "the market," cue jazz hands, to ensure access to my music, especially when I have a solution that's already working that isn't subject to those risks.
But to add something substantive, I also do this with many artists. I also really like Tool, which are notoriously absent from all the platforms. I ripped my old CDs and uploaded them to Google Play Music and now I can listen whenever, wherever I want.